In some of the world's most highly populated areas, such as northern India and Bangladesh, and areas to the west of the Andes in South America, water supplies are critically dependent on glacier melt. The glaciers in these regions act to buffer periods of seasonally low flows, since glacier melt is highest during warm (and often dry) conditions when other sources of runoff are lowest. Yet many of these glaciers are receding, and in some cases, are expected to disappear altogether within the next 50
years. While glacier melt in these regions may contribute a relatively small part of the annual flow, it often contributes a substantial part of low flows, which typically occur during the time of year when water demand is highest. Furthermore, glacier melt counteracts droughts, due to the same feedback mechanism that causes glacier melt to buffer seasonally low flows. As glaciers recede due (at least in part) to warmer temperatures, melt rates become higher, initially leading to increased summer flows. Eventually though, the increased melt rates are more than counteracted by reductions in glacier area, leading to decreased summer flows, and eventually to loss of the glacier contribution altogether.
The overarching science question that this proposal addresses is: How have changes in headwater glaciers affected water supply reliability in those parts of the world where streamflow dynamics are most affected by glacier sources? We will address this question through the integration of a glacier model developed by co-I Clarke at the University of British Columbia with a spatially distributed hydrology model (DHSVM) developed by PI Lettenmaier and his group at the University of Washington. The integrated model will have the capability to represent glacier dynamics and runoff production over partially glacierized river basins with drainage areas up to approximately 5000 km2. The model will be initialized using satellite-based estimates of glacier extent (from ASTER, TM, and MSS) to be assembled by co-I Nolin at Oregon State University; these data will also be used to test model predictions of glacier evolution since the 1970s in three test river basins. The test basins will be selected to represent three areas globally where glacier effects on water supply are of greatest concern: northwestern North America, the Andes region of South America, and the "High Asia" region. In addition to reconstructing, using the integrated modeling framework, glacier extent and streamflow for the three test basins, we will simulate conditions over the next century using downscaled climate model simulations. We will then use water resource systems analysis techniques to evaluate the effects of ongoing and projected future glacier changes on water supply reliability, and we will evaluate the potential for reservoir storage to balance the effects of receding glaciers on water supply in the test basins.
This proposal responds directly to subelement 3 of the NRA (Hydrologic, biological, biogeochemical, and geological impacts of melting ice) and specifically to the area Implications of reduced mountain glacier extent for river flow and subsequent effects on terrestrial biological productivity, biodiversity, and/or water availability.... We note that the UN Millenium Development Goals aspire to reduce, by 2015, the estimated 1 billion people globally who do not to have an adequate source of water supply. The effects of receding glaciers complicate this effort. The proposed research is directly relevant in this respect to Subgoal 3A in NASA's Strategic Plan, Study earth from space to advance scientific understanding and meet societal needs.